Photobiomolecular deposition of metallic particles and films

ABSTRACT

The method of the invention is based on the unique electron-carrying function of a photocatalytic unit such as the photosynthesis system I (PSI) reaction center of the protein-chlorophyll complex isolated from chloroplasts. The method employs a photo-biomolecular metal deposition technique for precisely controlled nucleation and growth of metallic clusters/particles, e.g., platinum, palladium, and their alloys, etc., as well as for thin-film formation above the surface of a solid substrate. The photochemically mediated technique offers numerous advantages over traditional deposition methods including quantitative atom deposition control, high energy efficiency, and mild operating condition requirements.

BACKGROUND OF THE INVENTION

[0001] This invention relates generally to metallic particles and films,and more particularly to methods for their production by linking theelectron pumping features of certain biological systems, such as thephotosynthetic machinery, with the reductive precipitation of metallicparticles.

[0002] Photosynthesis is the biological process that convertselectromagnetic energy into chemical energy through light and darkreactions. In green algae and higher plants, photosynthesis occurs inspecialized organelles, called chloroplasts. The chloroplast is enclosedby a double membrane and contains thylakoids, consisting of stackedmembrane disks (called grana) and unstacked membrane disks (calledstroma). The thylakoid membrane contains two key photosyntheticcomponents, photosystem I and photosystem II, designated PSI and PSII,respectively, as depicted schematically in FIG. 1. Duringphotosynthesis, water is split into molecular oxygen, protons andelectrons by PSII. Electrons derived from the splitting of watermolecules are transported through a series of carriers to PSI where theyare further energized by a light-induced photochemical charge separationand transported across the thylakoid membrane where they are used forthe enzymatic reduction of NADP⁺ to NADPH. This biological reaction isfurther utilized for chemical energy production, primarily in the formof ATP.

[0003] Ultrafine metallic particles, e.g., nanoparticles, are importantprecursors for use in the fabrication of advanced material structures,such as thin continuous films. Conventionally, metallic films have beendeposited on substrates by methods such as chemical vapor deposition(CVD), sputtering, plating, and the like. Unfortunately, such methods donot generaly offer a degree of control desired for the deposition ofnanostructured materials, e.g., films having nanometer range thicknessesor grains. Therefore, a method which could drive the nucleation, growthand deposition of nanoparticles in a quantitative, rapid, andenergy-efficient manner would be highly desirable for many applications,including materials processing, catalysis, separations, electronics,energy production processes, and environmental applications.

[0004] Despite the extensive investigation concerning the photosyntheticmachinery, the use of photosynthesis-related principles for materialssynthesis and processing has not been described. The present invention,by exploiting the electron pumping characteristics of the photosyntheticmachinery for nanoparticle production and processing applications,provides improved methods and materials which overcome or at leastreduce the effects of one or more of the aforementioned problems.

SUMMARY OF THE INVENTION

[0005] This invention broadly concerns methods for the controlleddeposition of ultrafine metallic particles and thin films viabiomolecular electronic mechanisms. In particular, the invention takesadvantage of the electron-pumping characteristics of photosynthesissystem I (PSI), and other biological systems having similar features,for photocatalytically reducing metal precursor chemicals into metallicnanostructured materials.

[0006] Therefore, according to one aspect of the invention, a metallicfilm is formed by providing a liquid suspension which is at least partlycomprised of a plurality of photosystem I-containing units, metalprecursors, and any other component necessary or desired for effectingthe photochemical reaction on the PSI-containing unit, e.g., electrondonor molecules. The liquid suspension is contacted with light,preferably in the form of intermittent flashes, under conditionseffective for causing the controlled reductive precipitation of themetal precursors on the photosystem I-containing units to formphotosystem I-metal complexes. Generally, the liquid suspensioncontaining the photosystem I-metal complexes is provided above thesurface of a solid or semisolid substrate, such as a surface comprisedof gold, silicon, silica, alumina, zirconia, titania, or any of avariety of other materials. Thereafter, the liquid of the liquidsuspension is removed, for example by applying heat and/or vacuum toevaporate the liquid. Upon removal of the liquid, a film is therebyformed on the surface of the substrate that is at least partly comprisedof the metal from the photosystem I-metal complexes.

[0007] In another aspect of the invention, a plurality of PSI-containingunits may be anchored or otherwise coated on a desired substrate priorto performing the photo-induced formation of the photosystem I-metalcomplexes. This PSI-coated substrate is then contacted with a solutioncontaining a plurality of metal precursors, electron donor molecules andother desired components. The solution and the underlying PSI-coatedsubstrate are thereafter contacted with light energy under conditionseffective for causing the reductive precipitation of the metal precusoron the photosystem I-containing unit to form photosystem I-metalcomplexes that are spatially constrained along the surface of thesubstrate. Under appropriate reaction conditions, the metal particles onthe PSI-containing units are controllably grown to a size at which metalparticles on adjacent PSI-containing units above the substrate mergeinto a continuous metallic film.

[0008] In another aspect of the invention, metallic nanoparticles areprovided by forming PSI-metal complexes in a suitable liquid suspensionand thereafter separating the metal particles from the PSI-metalcomplexes. The means by which the metal particles are separated mayinclude any suitable chemical, physical or mechanical treatmentsufficient to remove the particles from the complexes without adverselyaffecting their chemical composition or structural integrity.

[0009] The methods of the present invention offer numerous advantagesover other technologies, e.g., CVD, sputtering, electroless plating,MBE, etc., for the production of metallic particles, films, and othermaterials such as alloys and composites. First the methods allow forprecisely controlled metal particle nucleation and growth foratomic-level deposition. The methods are energy-efficient and have norequirement for high temperature or pressure/vacuum systems, such as arerequired for other technologies. Moreover, the methods offercontrollable deposition kinetics which may be varied through modulationof the light energy input level. Finally, the methods areenvironmentally benign and non-interfering, i.e, light is thecontrolling mechanism.

[0010] The nanosized particles of this invention, and the productsderived therefrom, will support a broad range of applications, includingenergetics (e.g., as fuel in propellants), explosives, microelectronics,catalysis, powder metallurgy, coating and joining technologies, andothers. For example, for catalysis/separations applications, reductionsin metallic film thicknesses will reduce metal cost, allow higherhydrogen flux, enhance permselectivity, and improve membrane reactorefficiency. The membrane reactors have been used in energy generationand environmental application processes, such as the advanced powergeneration and environmental application processes, such as the advancedpower generation systems-integrated gasification combined cycle (IGCC)systems.

[0011] In the petrochemical industry, important applications may includehydrogen separation and membrane reactions concerning hydrocarbon (suchas propane and ethylbenzene) dehydrogenation and natural gas steamreforming (e.g., CH₄+H₂O→CO+3H₂), oxidative reforming of methane tosyngas, and partial oxidation or oxidative coupling of methane intohydrogen and higher hydrocarbons. For these chemical reactions,palladium (Pd)-based membranes may be preferred in terms of temperatureresistance and hydrogen permeability, however other metals, e.g.,platinum and osmium, may also be used. In addition, metallicnanoparticle arrays of uniform particle size in the range of about2.5-100 nm deposited over a large area oxide (1 cm²) support offerpromising alternatives to single crystal surface catalysts.

[0012] The methods of the invention also find use in a variety ofapplications involving electronic materials and devices, such aselectronic circuit board fabrication, metallic (Pd) buffer layerpreparation for superconducting RABiTS (Rolling-Assisted BiaxiallyTextured Substrate), and multilayer devices (such as hard disk readinghead memory chip) based on GMR (Giant Magnetorresistance).

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention may be best understood by reference to thefollowing description taken in conjunction with the accompanyingdrawings in which:

[0014]FIG. 1 depicts schematically a simplified representation oflight-induced electron transport through the photosynthetic machinery ofthe thylakoid membrane;

[0015]FIG. 2 illustrates the production of a light-induced PSI-metalcomplex in a liquid suspension which contains metal precursors, electrondonors and PSI-containing units. The metal precursors in the suspensionundergo reductive precipitation at the reducing end of PSI to form ametal particles, the sizes of which may be controlled by the amount oflight provided; and

[0016]FIG. 3 illustrates one embodiment of the invention whereinPSI-containing units are coated/anchored on a suitable substrate. ThePSI-coated substrate is contacted with a solution containing metalprecursors and electron donor molecules, and light energy is appliedunder condition for forming the desired PSI-metal complexes. As themetal particles of the PSI-metal complexes grow larger in response to acontinued application of light energy, the particles can merge bybiomolecular “welding” to form a continuous metal film over thesubstrate.

[0017] While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the invention to the particularforms disclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

[0018] Illustrative embodiments of the invention are described below. Inthe interest of clarity, not all features of an actual implementationare described in this specification. It will of course be appreciatedthat in the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

[0019] According to the present invention, metallic nanoparticles andfilms are produced by light-mediated reactions between the reducing endof a PSI-containing unit and metal precursor compounds. The reactionsare generally carried out in a liquid suspension containing metalprecursor compounds and electron donor molecules such that thephotoelectrodeposition and nanoparticle growth is induced on thereducing end of PSI reaction centers by the controlled administration oflight energy. For example, by using a pulsed light source, metalprecipitation on the reducing end of PSI, and consequently the size ofmetal particles generated, can be controlled at the atomic level, e.g.by precise deposition of one metal atom at a time.

[0020] Metallic nanoparticles, or metallic particles, as the terms areused herein, refer to the those particles attainable by the methods ofthe invention. The size of the nanoparticles so produced are notstrictly limited, and may range, for example, from less than 1 nm togreater than 1000 nm or more. However, certain advantages may berealized when the nanoparticles have diameters in the range of about 1nm to 100 nm. Preferably, the nanoparticles will have diameters in therange of about 1 nm to 10 nm. The metallic nanoparticles may beseparated from the PSI-containing units after they are produced or maybe used while still coupled to the PSI-containing units, depending onthe particular application.

[0021] The PSI-containing units used in accordance with the presentinvention will preferably be comprised of isolated thylakoids or PSIparticles prepared, for example, from spinach chloroplasts. Methods forthe isolation and preparation of thylakoids and PSI particles are wellknown in the art (see, for example, Boardman, 1971; Setif et al., 1980;Reeves and Hall, 1980). Of course other PSI-containing units orphotoelectron pumping units may also be used. For example, thePSI-containing unit may be comprised of any of a variety of combinationsof photosynthetic and/or other cellular or non-cellular componentsprovided the PSI-containing unit contains the components necessary foreffecting reductive precipitation of the desired metal precursor. ThePSI-containing unit, as the phrase is used in the context of thisinvention, may include other electron pumping cellular machineries fromplant or non-plant organisms. The skilled individual will appreciatethat other biological photochromic units (such as PSII, bacteriallight-sensitive proteins, bacteriorhodopsin, photocatalyticmicroorganisms, and algae) or a biotic photocatalytic unit such as TiO₂and pigments (e.g., proflavine and rhodopsin), may be suitable sincethese systems also possess a mechanism for light-induced electronpumping. Moreover, one could also produce electron pumping systems usingself-assembled-monolayers containing light sensitive organic dyes.

[0022] PSI is a protein-chlorophyll complex that is part of thephotosynthetic machinery within the thylakoid membrane (see FIG. 1). Itis ellipsoidal in shape and has dimensions of about 5 by 6 nanometers.The photosystem I reaction center/core antenna complex contains about 40chlorophylls per photoactive reaction center pigment (P700). Thechlorophyll molecules serve as antennae which absorb photons andtransfer the photon energy to P700, where this energy is captured andutilized to drive photochemical reactions. In addition to the P700 andthe antenna chlorophylls, the PSI complex contains a number of electronacceptors. An electron released from P700 is transferred to a terminalacceptor at the reducing end of PSI through intermediate acceptors, andthe electron is transported across the thylakoid membrane.

[0023] Natural photosynthetic systems have been modified to containcolloidal metallic platinum at the reducing site of PSI in thylakoidmembranes in order to make metallic catalyst systems (see, for example,Greenbaum, 1985; Greenbaum, 1988; Greenbaum, 1990; Lee et al., 1990; Leeet al., 1994). In these reactions, molecular hydrogen is synthesizedthrough reduction of protons by a reaction that is catalyzed by theplatinum colloidal particles adjacent to the reducing site of PSI on thestromal side of the thylakoid membrane. Platinization of PSI can beaccomplished through either chemical precipitation (such as platinumprecipitation by H₂ purging) or preferably by in-situ photochemicalreduction of platinum chemical precursors into metallic platinumcolloid. Both chemical and in-situ photogenic reductive precipitation ofmetal platinum occur in close proximity to the PSI reducing end,indicating that metal precursors (e.g., [Pt(Cl)₆]²⁻) have high affinityfor the PSI reducing end (Greenbaum 1988; Lee et al., 1994). It has beenshown that the platinization process does not impede the intrinsicphotosynthetic activity, e.g., electron transport (Greenbaum, 1990; Leeet al., 1995), and that the properties of PSI reaction centers arestable under relatively long-term storage (Lee et al., 1995).Importantly, because hydrogen is synthesized during the photoreductiveprecipitation reactions described herein, hydrogen evolution can be usedas a sensitive indicator of metal particle formation on PSI (Greenbaum,1988).

[0024] A film, as the term is used herein, refers to a film or coatingat least partly comprised of and/or made from the nanoparticlesdescribed herein. Typically, the film will be supported by a solidsubstrate, such as those comprised of metal or ceramic, e.g., gold,silicon, silica, titania, zirconia, and the like. For most applications,the films will have a thickness in the range of about 1 nm to 5000 nm.Because of the high degree of control offered by this invention, highquality films in the range of about 1 nm to 100 nm are preferablyproduced. The metallic films produced according to the invention may beformed as composites or alloys with other materials. Additionally, theymay contain residual proteinaceous material as a result of the presenceof PSI-containing units present during some film forming processes.

[0025] In one embodiment of the present invention, a method is providedfor producing films from metallic nanoparticles using liquid suspensionscomprised of photosystem I-containing units, metal precursor compoundsand electron donor compounds. Additional components may also be presentin the liquid suspension, for example, organic monomers, depending onthe requirements and/or preferences of a given application. The liquidsuspension is contacted with light under conditions in which the metalprecursor undergoes reductive precipitation at the reducing end of thePSI particle of the PSIA-containing unit. As a result, metallicparticles are provided in the form of photosystem I-metal complexes inthe liquid suspension. The size of the metallic particles in thePSI-metal complexes is directly related to amount and intensity of lightenergy administered. Consequently, particles having desired dimensionsmay be controllably synthesized.

[0026] The PSI-metal complexes are provided above a solid substrate,typically by applying a volume of the suspension on the surface of thesubstrate. The substrate may be one upon which the liquid suspension waspreviously applied prior to formation of the PSI-metal complexes.Alternatively, the PSI-metal complexes may be formed in a separateliquid suspension vessel and the liquid suspension may be thereafterapplied above the substrate surface. In one preferred approach, sol/geltechniques are used wherein the substrate is dipped directly into theliquid suspension containing the PSI-metal complexes or the liquidsuspension containing the PSI-metal complexes is spin coated onto thesubstrate. Such methods may be preferred where a high degree ofthickness control is desired. Substantially all of the liquid present inthe liquid suspension is removed from the coated substrate, for exampleby air drying or by applying heat, vacuum, etc., to cause evaporation ofthe liquid. This provides on the surface of the substrate a filmcomprised primarily of PSI-metal complexes.

[0027] Films having a variety of structural features may be obtained bythis approach. For example, microporous films may be produced by coatingthe substrate with a liquid suspension comprised of a mixture ofPSI-metal complexes wherein the PSI-containing units are thylakoids.Alternatively, nanoporous films may be provided by using liquidsuspension containing PSI-metal complexes wherein the PSI-containingunits are isolated PSI particles. Thus, the size of the biologicalcomponents present in the PSI-metal complexes will determine to someextent the size of the pores in the materials following removal of thebiological components from the films, e.g., by sintering. In addition,dense nanophase films can be provided by coating on the substrate asolution containing substantially pure metallic nanoparticles which havebeen separated from the PSI-metal complexes.

[0028] According to another embodiment of the invention, metallic filmfabrication can be achieved on an ordered layer of PSI-containing unitsanchored or otherwise coated on the surface of a substrate (such asgold, silicon, alumina, etc.). These PSI-coated substrates have beendescribed (see, for example, Rutherford and Sétif, 1990; Lee et al.,1996; and Lee et al, 1995). The types of interactions (e.g., covalent,electrostatic, etc.) between the PSI-containing units and the substrateare not critical provided they are substantially stable in the liquidsuspensions in which the photoreactions will be performed and they donot preclude the availability of the reducing end of the PSI unit forreductive metal precipitation.

[0029] The PSI-coated substrate is contacted with a solution (or,alternatively, could be exposed to vapor) that contains the desiredmetal precursor compounds and electron donor molecules. Light exposureof the PSI-containing units on the substrate leads to the reductiveprecipitation of the metal, as described above. However, in thisembodiment, metal particle formation is spatially constrained along thesurface of the substrate where the PSI-containing units are anchored. Bycontrolling the input of light energy and the number of light pulses,and therefore particle growth, a biomolecular “welding” effect may beachieved on the PSI-coated layer, in which adjacent metallic particlesprecipitated on the PSI-containing units grow sufficiently large andeventually coalesce into a continuous metal film. The size of metalparticles and the thickness of the film that is formed can therefore beprecisely controlled by exposing an appropriate amount of light energyon the photoreactor system. Of course, the light input required to forma film having a desired thickness will depend to some extent on thedensity of the PSI-containing units coated on the substrate prior tolight-induced metal precipitation.

[0030] Although thick films may be produced according to these methods,thin films having nanometer range thicknesses, e.g., 1 to 10 nm, arepreferably synthesized to take advantage of the precise depositioncontrol offered by this invention. None of the traditional film-formingtechnology, such as CVD, PVD, sputtering, or epitaxial growth canprovide a comparable level of control. Moreover, the films of thisinvention can be advantageously provided as patterned metal layers usingconventional photolithographic techniques.

[0031] In another embodiment of the invention, a method is provided forthe production of metallic nanoparticles. In this approach, desiredPSI-metal complexes are formed as described in the above embodiments.However, the PSI-metal complexes are not applied to a substrate toeffect film formation. Rather, after the light induced reductiveprecipitation reactions, the PSI-metal complexes are treated in a mannerwhich allows for the separation of metallic particles from thePSI-containing units. This can be accoplished by any of a number ofapproaches. For example, the PSI-metal complexes could be treated withvarious surfactants, e.g., sodium dodecyl sulfate (SDS), or could besubjected to sufficent agitation, ultrasonication, etc., in order todisrupt the association between the metal particles and the PSI-units.Alternatively, the biological components present in the PSI-metalcomplexes could be solubilized with an organic solvent or degraded usingenzymatic reactions, e.g., using nucleases, proteases, etc, to removethe metal particles provided the treatment does not unacceptablycompromise the integrity of the particles. Upon dissociation of themetal particles from the PSI-units using an approach such as thosedescribed above, the metal particles can be readily separated by one ormore density-based separation techniques.

[0032] The metal precursor compounds used in conjunction with thisinvention can include any of a variety of compounds capable ofundergoing reductive precipitation to form a desired metallic species.The metal precursors will typically comprise ionic metal salts capableof accepting electrons from PSI such that upon transfer of one or moreelectrons, the metal precursors are reduced to a pure metal form.Suitable metal precursors for producing the metallic particles of theinvention may include, without limitation, ionic salts of platinum,palladium, osmium, ruthenium, iridium, silver, copper, indium, nickel,iron and tin, such as chloride-derived, sulfate-derived andnitrate-derived salts of these and related metals. Particularlypreferred metal precusors for use in the invention includehexachloroplatinate ([PtCl₆]²⁻), hexachloroosmiate ([OsCl₆]²⁻), andhexachloropalladinate ([PdCl₆]²⁻).

[0033] The electron donor molecules which are included in the liquidsuspensions according to the invention should of course be compatiblewith the PSI electron pumping system that is employed. The electrondonor in most applications will be water, however some organic moleculesmay be present in the liquid suspensions which serve as facilitators ofthe electron transport process. These may include, for example, EDTA,proflavin, methylviologen, and the like. The concentration of thesefacilitator molecules, when present, will typically be in the range ofabout 10 mM to 100 mM in the liquid suspension.

[0034] Essentially any light source may be used in accordance with theinvention provided it can generate light in a visible portion of thesolar emission spectrum. Typically, the wavelengths of light mosteffective for causing PSI electron pumping activity will be betweenabout 400 and 700 nm. Although the light exposure of the PSI-containingunits may be continuous, it will generally be preferred to useintermittent pulses/flashes of light given the level of control thisprovides over particle growth. Intermittent illumination with a pulsedflash light source (e.g., a stroboscopic flash lamp) can providequantitative control of the deposition at the reducing sites of PSI, onemetallic atom at a time. Numerous such light sources are available, suchas the GenRad Model 1539A xenon flash lamp. Preferably, the flash lampsare coupled with a trigger generator, such as the Hewlett Packard Model8011A. This device allows the frequency of the trigger pulses to bevaried from 1 to 400 Hz, the range of frequencies over which the xenonflash lamps may be fired without degrading light output.

[0035] In addition to the nanoparticles and continuous thin filmsdescribed above, metallic patterns of nanoscale resolution may beprepared on a substrate surface by coupling laser and/or electron beamlithography techniques with the methods of this invention. For example,a position-controllable laser beam could be used to provide precisedeposition of metal particles and/or lines in essentially any desiredpattern on the surface of a PSI-coated substrate.

[0036] If the substrate on which the deposition is performed is aceramic, the invention can be readily adapted for the fabrication ofvarious types of metal-ceramic membranes, e.g., (1) dense or porousmetallic membranes that are supported on porous ceramic membranes; (2)metals deposited inside the pores of ceramic membranes; and (3) metalscoated on solid particles that are partially sintered onto inorganicmembranes.

[0037] The following example is provided to illustrate one embodiment ofthis invention. The techniques disclosed in the example which followsrepresent those projected by the inventors to function in the practiceof the invention and thus can be considered to constitute an example ofone mode for its practice. However, those skilled in the art should, inlight of the present disclosure, appreciate that many changes can bemade in the specific embodiments which are disclosed and still obtain alike or similar result without departing from the spirit and scope ofthe invention.

EXAMPLES

[0038] Photobiomolecular Deposition of a Platinum Film

[0039] Type C chloroplasts are isolated according to the method ofReeves and Hall (1980). In this preparation, the chloroplast envelope isosmotically ruptured, exposing the thylakoid membranes to the externalaqueous medium. The thylakoids are suspended in Walkers assay medium andadjusted to a final chlorophyll concentration of about 3 mg. A solutionof chloroplatinic acid neutralized to pH 7 is added in the dark to thethylakoid suspension to give a final concentration of 1 mM in thesuspension (this value is not critical provided there is an excess ofhexachloroplatinate ions to photosystem I reaction centers). The liquidsuspension is illuminated with a xenon stroboscopic light source (GenRadType 1539) set to be triggered by a pulse generator (Hewlett-Packard8011A). The frequency of the flashing is 10 Hz and the duration is 3μsec at half height. Pulsed light exposure of the suspension isperformed for 90 minutes. Following the light treatment of thesuspension to form the desired PSI-metal complexes, the suspension isspin coated on a silicon substrate at about 25° C. to provide thedesired film. The PSI-film so produced will exhibit photocatalyticproperties and vectorial electron transport, and will be useful, forexample, as a photocatalyst.

[0040] The particular embodiments disclosed above are illustrative only,as the invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. More specifically, it will be apparentthat certain compounds that are chemically, structurally and/orfunctionally related to those disclosed herein may be substituted in themethods of this invention while the same or similar results would beachieved. Furthermore, no limitations are intended to the details ofconstruction or design herein shown, other than as described in theclaims below. It is therefore evident that the particular embodimentsdisclosed above may be altered or modified and all such variations areconsidered within the scope and spirit of the invention. Accordingly,the protection sought herein is as set forth in the claims below.

[0041] References

[0042] Boardman, Methods Enzymol, 23:268, 1971.

[0043] Greenbaum, “Platinized chloroplasts: a novel photocatalyticmaterial,” Science, 230(4732):1373, 1985.

[0044] Greenbaum, “Interfacial photoreactions at the photosyntheticmembrane interface: an upper limit for the number of platinum atomsrequired to form a hydrogen-evolving platinum metal catalyst,” J. Phys.Chem., 92:4571, 1988.

[0045] Greenbaum, “Biomolecular electronics: observation of orientedphotocurrents by entrapped platinized chloroplasts,” Bioelectrochemistryand Bioenergetics, 21:171, 1989.

[0046] Greenbaum, “Vectorial photocurrents and photoconductivity inmetalized chloroplasts,” J. Phys. Chem., 94:6151, 1990.

[0047] Greenbaum, “Kinetic studies of interfacial photocurrents inplatinized chloroplasts,” J. Phys. Chem., 96:514, 1992.

[0048] Lee, Tevault, Blankinship. Collins, Greenbaum, “Photosyntheticwater splitting: in-situ photoprecipitation of metallocatalysts forphotoevolution of hydrogen and oxygen,” Energy & Fuels, 8:770, 1994.

[0049] Lee, Lee, Warmack, Allison, Greenbaum, “Molecular electronics ofa single photosystems I reaction center: studies with scanning tunnelingmicroscopy and spectroscopy,” Proc. Natl. Acad. Sci. USA, 92:1965, 1995.

[0050] Lee and Greenbaum, “Bioelectronics and biometallocatalysis forproduction of fuels and chemicals by photosynthetic water splitting,”Appl. Biochem. Biotechnol., 51(52):295, 1995.

[0051] Lee, Lee, Greenbaum, “Platinization: a novel technique to anchorphotosystem I reaction centers on a metal surface at biologicaltemperature and pH,” Biosensors & Bioelectronics,, 11(4):375, 1996.

[0052] Reeves, S. G.; Hall, D. O., Methods Enzymol. 69: 85-94, 1980.

[0053] Rutherford and Sétif, “Orientation of P700, the primary electrondonor of photosystem I,” Biochimica et Biophysica Acta, 1019:128, 1990.

[0054] Sétif, Acker, Lagoutte, Duranton, Photosynth. Res., 1:17, 1980.

What is claimed:
 1. A method for producing a metallic film on asubstrate surface, comprising: providing in a liquid suspension aplurality of photosystem I (PSI)-containing units and metal precursors;contacting said liquid suspension with light under conditions effectivefor causing the reductive precipitation of metal precursors on thephotosystem I-containing units to form photosystem I-metal complexes;and providing said photosystem I-metal complexes above a substratesurface to form a film.
 2. The method of claim 1, wherein the metalprecursor is comprised of an ionic metal salt, wherein the metal of saidionic metal salt is selected from the group consisting of platinum,palladium, osmium, ruthenium, iridium, silver, copper, indium, nickel,iron and tin.
 3. The method of claim 1, wherein the metal precursors areselected from the group consisting of hexachloroplatinate ([PtCl₆]²⁻),hexachloroosmiate ([OsCl₆]²⁻) and hexachloropalladinate ([PdCl₆]²⁻). 4.The method of claim 1, wherein the liquid suspension contains one ormore components which facilitate electron transport through saidPSI-containing units.
 5. The method of claim 1, wherein thePSI-containing units are comprised of isolated PSI particles.
 6. Themethod of claim 1, wherein the PSI-containing units are comprised ofisolated thylakoids.
 7. The method of claim 1, wherein the substrate isselected from the group consisting of gold, silica, alumina, zirconia,titania, silicon, glass and plastic.
 8. The method of claim 1, whereinat least some of the light contacted with said liquid suspension has awavelength in the range of about 400 nm to 700 nm.
 9. The method ofclaim 1, wherein the light contacted with said liquid suspension isadministered as intermittent flashes.
 10. The method of claim 9, whereinthe intermittent flashes are administered at a frequency in the range of1 to 100 hz.
 11. The method of claim 1, wherein the PSI-metal complexesare provided on the substrate surface by spin coating or dip coating.12. The method of claim 1, further comprising providing a treatment todegrade at least some of the PSI-containing units within the film. 13.The method of claim 1, wherein the film has a thickness in the range ofabout 1 to 10 nm.
 14. A film produced according to the method ofclaim
 1. 15. A method for producing a metallic film on a substratesurface, comprising: providing in a liquid suspension a plurality ofphotosystem I (PSI)-containing units and metal precursors, wherein themetal precursors are comprised of an ionic salt of a metal selected fromthe group consisting of platinum, palladium, osmium, ruthenium, iridium,silver, copper, indium, nickel, iron and tin; contacting said liquidsuspension with light under conditions effective for causing thereductive precipitation of metal precursors on the photosystemI-containing units to form photosystem I-metal complexes; and providingsaid photosystem I-metal complexes above a substrate surface to form afilm.
 16. The method of claim 15, wherein the metal precursors areselected from the group consisting of hexachloroplatinate ([PtCl₆]²⁻),hexachloroosmiate ([OsCl₆]²⁻) and hexachloropalladinate ([PdCl₆]²⁻), 17.The method of claim 15, wherein the substrate is selected from the groupconsisting of gold, silica, alumina, zirconia, titania, silicon, glassand plastic.
 18. The method of claim 15, wherein the film has athickness in the range of about 1 nm to 10 nm.
 19. A film producedaccording to the method of claim
 15. 20. A method for producing ametallic film on a substrate surface, comprising: providing in a liquidsuspension a plurality of photosystem I (PSI)-containing units and metalprecursors, wherein the metal precursors are selected fromhexachloroplatinate ([PtCl₆]²⁻), hexachloroosmiate ([OsC₆]²⁻) andhexachloropalladinate ([PdCl₆]²⁻); contacting said liquid suspensionwith light under conditions effective for causing the reductiveprecipitation of metal precursors on the photosystem I-containing unitsto form photosystem I-metal complexes; and providing said photosystemI-metal complexes above a substrate surface to form a film.
 21. Themethod of claim 20, wherein the substrate is selected from the groupconsisting of gold, silica, alumina, zirconia, titania, silicon, glassand plastic.
 22. The method of claim 20, wherein the film has athickness in the range of about 1 nm to 10 nm.
 23. A film producedaccording to the method of claim
 20. 24. A method for producing ametallic film on a substrate surface, comprising: providing a substratesurface having coated thereon a plurality of photosystem I(PSI)-containing units; providing a liquid suspension above thesubstrate surface, said liquid suspension containing a plurality ofmetal precursors; and contacting the PSI-containing units with lightunder conditions effective for causing the reductive precipitation ofthe metal precusor on the photosystem I-containing unit to formphotosystem I-metal complexes.
 25. The method of claim 24, wherein themetal precursor is comprised of an ionic metal salt, wherein the metalof said ionic metal salt is selected from the group consisting ofplatinum, palladium, osmium, ruthenium, iridium, silver, copper, indium,nickel, iron and tin.
 26. The method of claim 24, wherein the metalprecursors are selected from the group consisting of hexachloroplatinate([PtCl₆]²⁻), hexachloroosmiate ([OsCl₆]²⁻) and hexachloropalladinate([PdCl₆]²⁻).
 27. The method of claim 24, wherein the PSI-containingunits are comprised of isolated PSI particles.
 28. The method of claim24, wherein the PSI-containing units are comprised of isolatedthylakoids.
 29. The method of claim 24, wherein the substrate isselected from the group consisting of gold, silica, alumina, silicon,glass, plastic and titania.
 30. The method of claim 24, wherein at leastsome of the light contacted with said liquid suspension has a wavelengthin the range of about 400 nm to 700 nm.
 31. The method of claim 24,wherein the light contacted with said liquid suspension is administeredas intermittent flashes.
 32. The method of claim 31, wherein theintermittent flashes are administered at a frequency in the range of 1to 100 hz.
 33. The method of claim 24, further comprising providing atreatment to degrade at least some of the PSI-containing units withinthe film.
 34. The method of claim 24, wherein the film has a thicknessin the range of about 1 to 10 nm.
 35. A film produced according to themethod of claim
 24. 36. A method for producing a metallic film on asubstrate surface, comprising: providing a substrate surface havingcoated thereon a plurality of photosystem I (PSI)-containing units;providing a liquid suspension above the substrate surface, said liquidsuspension containing a plurality of metal precursors, wherein the metalprecursor is comprised of an ionic salt of a metal selected from thegroup consisting of platinum, palladium, osmium, ruthenium, iridium,silver, copper, indium, nickel, iron and tin; and contacting thePSI-containing units with light under conditions effective for causingthe reductive precipitation of the metal precusor on the photosystemI-containing unit to form photosystem I-metal complexes.
 37. The methodof claim 36, wherein the substrate is selected from the group consistingof gold, silica, alumina, zirconia, titania, silicon, glass and plastic.38. The method of claim 36, wherein the film has a thickness in therange of about 1 nm to 10 nm.
 39. A film produced according to themethod of claim
 36. 40. A method for producing a metallic film on asubstrate surface, comprising: providing a substrate surface havingcoated thereon a plurality of photosystem I (PSI)-containing units;providing a liquid suspension above the substrate surface, said liquidsuspension containing a plurality of metal precursors, wherein the metalprecursor is selected from hexachloroplatinate ([PtCl₆]²⁻),hexachloroosmiate ([OsCl₆]²⁻) and hexachloropalladinate ([PdCl₆]²⁻); andcontacting the PSI-containing units with light under conditionseffective for causing the reductive precipitation of the metal precusoron the photosystem I-containing unit to form photosystem I-metalcomplexes.
 41. The method of claim 40, wherein the substrate is selectedfrom the group consisting of gold, silica, alumina, zirconia, titania,silicon, glass and plastic.
 42. The method of claim 40, wherein the filmhas a thickness in the range of about 1 nm to 10 nm.
 43. A film producedaccording to the method of claim
 40. 44. A method for producing metallicparticles, comprising: providing in a liquid suspension a plurality ofphotosystem I (PSI)-containing units and metal precursors; contactingsaid liquid suspension with light under conditions effective for causingthe reductive precipitation of the metal precursor on the photosystemI-containing unit to form photosystem I-metal complexes; and separatingthe metal from the photosystem I-metal complexes to obtain metallicparticles.
 45. The method of claim 44, wherein the metal precursor iscomprised of an ionic salt of a metal selected from the group consistingof platinum, palladium, osmium, ruthenium, iridium, silver, copper,indium, nickel, iron and tin.
 46. The method of claim 44, wherein themetal precursors are selected from the group consisting ofhexachloroplatinate ([PtCl₆]²⁻), hexachloroosmiate ([OsCl₆]²⁻) andhexachloropalladinate ([PdCl₆]²⁻).
 47. The method of claim 44, whereinthe particles have diameters in the range of 1 to 1000 nm.
 48. Themethod of claim 44, wherein the particles have diameters in the range of1 to 10 nm.
 49. The method of claim 44, wherein the metal is separatedfrom the PSI-metal complexes by treatment with surfactants, mechanicalagitation, ultrasonication or enzymatic digestion.
 50. The method ofclaim 44, wherein the PSI-containing units are comprised of isolated PSIparticles.
 51. The method of claim 44, wherein the PSI-containing unitsare comprised of isolated thylakoids.
 52. The method of claim 44,wherein at least some of the light contacted with said liquid suspensionhas a wavelength in the range of about 400 nm to 700 nm.
 53. The methodof claim 44, wherein the light contacted with said liquid suspension isadministered as intermittent flashes.
 54. The method of claim 53,wherein the intermittent flashes are administered at a frequency in therange of 1 to 100 hz.
 55. A metallic particle produced according to themethod of claim
 44. 56. A method for producing metallic particles,comprising: providing in a liquid suspension a plurality of photosystemI (PSI)-containing units and metal precursors, wherein the metalprecursor is comprised of an ionic salt of a metal selected from thegroup consisting of platinum, palladium, osmium, ruthenium, iridium,silver, copper, indium, nickel, iron and tin; contacting said liquidsuspension with light under conditions effective for causing thereductive precipitation of the metal precursor on the photosystemI-containing unit to form photosystem I-metal complexes; and separatingthe metal from the photosystem I-metal complexes to obtain metallicparticles.
 57. The method of claim 56, wherein the metal precursors areselected from the group consisting of hexachloroplatinate ([PtCl₆]²⁻),hexachloroosmiate ([OsCl₆]²⁻) and hexachloropalladinate ([PdCl₆]²⁻). 58.The method of claim 56, wherein the particles have diameters in therange of 1 to 1000 nm.
 59. The method of claim 56, wherein the particleshave diameters in the range of 1 to 10 nm.
 60. A metallic particleproduced according to the method of claim
 56. 61. A method for producingmetallic particles, comprising: providing in a liquid suspension aplurality of photosystem I (PSI)-containing units and metal precursors,wherein the metal precursor is selected hexachloroplatinate ([PtCl₆]²⁻),hexachloroosmiate ([OsCl₆]²⁻) and hexachloropalladinate ([PdCl₆]²⁻);contacting said liquid suspension with light under conditions effectivefor causing the reductive precipitation of the metal precursor on thephotosystem I-containing unit to form photosystem I-metal complexes; andseparating the metal from the photosystem I-metal complexes to obtainmetallic particles.
 62. The method of claim 61, wherein the particleshave diameters in the range of 1 to 1000 nm.
 63. The method of claim 61,wherein the particles have diameters in the range of 1 to 10 nm.
 64. Ametallic particle produced according to the method of claim 61.